Which of the following is used to allocate memory dynamically in C?

Concept

Dynamic memory allocation lets a program request storage while it is running, when the required size or lifetime is not known at compile time.

In C, allocation functions are declared in the standard header <stdlib.h>, and allocated storage is accessed through a pointer.

Application

Consider reserving space for five integers at runtime.

1. Compute the required size as 5 * sizeof(int).

2. Call int *p = malloc(5 * sizeof *p);. The function requests one contiguous block of that many bytes and returns its starting address as a void * pointer, which C converts to int * on assignment.

3. Check p != NULL before using the block, because allocation can fail.

4. After use, call free(p); so the dynamically allocated block is released.

Cross-check and contrast

• alloc() is not an ISO C standard-library allocation function.

• create() is not an ISO C standard-library memory function; system APIs may use that name for other resources.

• new is a C++ allocation operator rather than a C function named new().

• malloc() is declared by ISO C for requesting a block of storage of a specified byte size.

Therefore, the required function is malloc().